1. Field of the Invention
The invention relates broadly to nanofiber packed beds having enhanced fluid flow characteristics and to methods of making same and methods of using same. More specifically, the invention relates to nanofibers which are uniformly or non-uniformly blended with supporting scaffold particulates to form packed beds having enhanced fluid flow rates and an increased overall average pore size. Even more specifically, the invention relates to using such packed beds for a variety of purposes including as products such as flow-through electrodes, chromatographic media, adsorbant media and filters.
2. Description of the Related Art
Nanofiber mats and assemblages have been previously produced to take advantage of the increased surface area per gram achieved using extremely thin diameter fibers. These prior mats or assemblages are either in the form of tightly, dense masses of intertwined fibers and/or are limited to microscopic structures (i.e., having a largest dimension less than 1 micron). Nanofiber mats or assemblages have been previously prepared by dispersing nanofibers in aqueous or organic mediums and then filtering the nanofibers to form a mat. The mats have also been prepared by forming a gel or paste of carbon fibrils in a fluid, e.g. an organic solvent such as propane and then heating the gel or paste to a temperature above the critical temperature of the medium, removing supercritical fluid and finally removing the resultant porous mat or plug from the vessel in which the process has been carried out. See, U.S. patent application Ser. No. 08/428,496 entitled "Three-Dimensional Macroscopic Assemblages of Randomly Oriented Carbon Fibrils and Composites Containing Same" by Tennent et al. hereby incorporated by reference.
One of the disadvantages of the prior assemblages or mats made by the above described methods is poor fluid flow characteristics within the structure. As suspensions of nanofibers are drained of the suspending fluid, in particular water, the surface tension of the liquid tends to pull the nanofibers into a dense packed "mat". Alternatively, the structure may simply collapse. The pore size of the resulting mat is determined by the interfiber spaces which as a result of the compression of these mats tend to be quite small. As a result, the fluid flow characteristics of such mats are poor.
Accordingly, although previous work has shown that nanofibers can be assembled into packed, thin, membrane-like assemblages through which fluid will pass, the small diameters of the nanofibers results in a very small pore structure that imposes a large resistance to fluid flow.
It would be desirable to overcome the above-mentioned disadvantages by producing a porous packed bed having enhanced fluid flow and an altered pore size distribution since there are applications for porous nanofiber packed beds that require fluid passage and the resistance to fluid transport creates serious limitations and/or drawbacks for such applications. The improved fluid flow characteristics brought about by this invention make such applications more feasible and/or more efficient.